Ncert xtract On Cell unit of Life
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CELL UNIT OF LIFE ,PROKARYOTIC CELL , EUKARYOTIC CELL , Biology
,Cell quick revision
Cell unit of life notes , Ncert xtract, Short notes on cells unit of life
1. Cell a Basic unit of life
2. Onion cell – Typical example of plant cell
3. Human cheek cell aTypical example of
animal cell
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4. The cell is the basic structure of organisms.
5. The environment outside the cell is separated
from the inside of the cell by the cell
membrane.
6. Unicellular organisms are capable of a
(i) independent existence and
(ii) performing the essential functions of life.
7. Anything less than a complete structure
of a cell does not ensure independent
living.
8. Cell a fundamental structural &
functional unit of all living organisms.
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CELL UNIT OF LIFE ,PROKARYOTIC CELL , EUKARYOTIC CELL , Biology ,Cell quick revision
Cell unit of life notes , Ncert xtract, Short notes on cells unit of lif
9. Anton Von Leeuwenhoek a
first saw and described a live cell.
Belongs to Holland
10. Robert Brown a discovered the nucleus.
11. CELL THEORY 1838 – 1839 a
Matthias Schleiden, a German botanist ;
Theodore Schwann , a British Zoologist,
12. Cell theory :
All living organisms are composed of cells and
products of cells.
All cells arise from pre-existing cells.
13. Rudolf Virchow (1855) -
Omnis cellula-e cellula
(New cells are formed from pre-existing cells)
14. Viruses are the biggest exception of cell
theory.
15. Type of Cells ->
Those have membrane bound nuclei
EUKARYOTIC
Those lack a membrane bound nucleus are
PROKARYOTIC.
16. The cytoplasm - >
MAIN ARENA OF CELLULAR ACTIVITY
Various chemical reactions occur in it to keep
the cell in the ‘living state’.
17. The prokaryotic cells lack membrane
bound organelles.
18. Ribosomes are non-membrane bound
organelles found in all cells
ell quick revision
Cell unit of life notes , Ncert xtract, Short notes on cells unit of life
19. Within the cell, ribosomes are also found à in
the two organelles –
Chloroplasts (in plants) & Mitochondria
20. Animal cells contain -> Another non-
membrane bound organelle --> centriole
-->Helps in cell division.
21. Size of Cells
Mycoplasmas, the smallest cells, (0.3 µm)
Bacteria (3 to 5 µm)
The largest isolated single cellà
Egg of an ostrich
Human red blood cells à
7.0 µm in diameter.
Nerve cells are the longest cells.
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22. The Prokaryotic cells -->
Bacteria,
Blue-green algae,
Mycoplasma and
PPLO (Pleuro Pneumonia Like Organisms).
23. Prokaryotes ---> Multiply more rapidly than the eukaryotic cells
24. The four basic shapes of bacteria
1 Bacillus (rod like),
2 Coccus (spherical),
3 Vibrio (comma shaped) and
4 Spirillum (spiral).
25. All prokaryotes have a cell wall ; except
mycoplasma.
26. Prokaryotes ---->
Nucleoid seen; no well-defined nucleus.
genetic material naked, single circular DNA
27. Bacteria have small circular DNA outside the
genomic DNA. ------> Plasmids.
The plasmid DNA confers Resistance to
antibiotics.
28. Nuclear membrane is found in eukaryotes.
29. Mesosome -------->
Characteristic of prokaryotes.
Infoldings of cell membrane.
Help in cell wall formation,
DNA replication & distribution to new cells.
Also help in respiration,
secretion processes, to increase the surface
area of the plasma membrane and enzymatic
content.
30. Most bacterial cells ----->
Have a chemically complex cell envelope.
Tightly bound three layered
Outermost glycocalyx then cell wall and then
the plasma membrane.
Glycocalyx -------> If loose sheath (slime
layer) or If thick and tough (Capsule)
31. Bacteria can be classified into two groups
On the basis of the differences in the cell
envelopes and the manner in which they
by Gram ------> Gram positive and Gram
negative bacteria.
32. The cell wall functions in Bacterial cell
determines the shape of the cell
Provides a strong structural support (prevent
bursting or collapsing)
33. The plasma membrane ------>
Selectively permeable
structurally similar in both prokaryotes
& eukaryotes.
34. Chromatophores ----->
present in prokaryotes like cyanobacteria,
Membranous extensions into the cytoplasm
which contain pigments.
35. Bacterial cells motility
May be motile or non-motile.
Thin filamentous extensions from their cell
wall called flagella.
Bacterial flagellum is composed of three
parts – filament, hook and basal body.
The filament is the longest portion and
extends from the cell surface to the
outside.
36. Pili and Fimbriae ---->
Surface structures of the bacteria
Do not play a role in motility.
The pili are elongated tubular structures
made of a special protein.
The fimbriae are small bristle like fibres
sprouting out of the cell.
Fimbriae are known to help attach the bacteria
to surface
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